BECKYHITCHIN
Bloomin ’ marvellous
We should embrace our annual plankton blooms , says Becky Hitchin , who sets out the ecological benefit of massed phytoplankton
We ’ re just past that time of year when social media feeds are full of laments that “ the viz has gone !”, that it ’ s “ 1m or less above 10m depth !”, or worse . You can sense the disappointment loaded into those few words . It ’ s time for the yearly spring plankton blooms , when 80 % of downloaded photos are full of more out of focus brown snot rather than what was going to be an award-winning picture of the nicest cup coral in the UK .
So what is this horrible brown snot , and why should we actually be grateful for its appearance every year ? It ’ s a concentration of many , many tiny microscopic organisms called phytoplankton that live suspended in the upper layers of the oceans . Phytoplankton comes in many types , some floating passively through the water , and some having the ability to influence where they are travelling with whip-like tails called flagella . Just like land plants , they take up carbon dioxide , make carbohydrates using light energy , and release oxygen . Because they need light , phytoplankton live near the surface of the seas and oceans , where enough sunlight can penetrate to allow photosynthesis .
While they are mainly microscopic , the influence of a large amount of them together can be enormous . If anyone ’ s marvelled at the cliffs of Dover after a good ( bloom-free ) dive in the English Channel , you ’ re marvelling at 110m of piled up phytoplankton , of a type called coccoliths . These coccoliths are made up of hard , saucer-shaped calcite plates around a soft body that sink and accumulate on the sea floor when the algae die , compacting and hardening into chalk over millions of years . It seems likely from recent research that algal blooms played a significant part for getting enough phytoplankton biomass into one place to start the development of the chalk cliffs .
Phytoplankton abundance and biomass is highly dependent on water conditions . In spring , more light becomes available and the surface water warms up . Mixing becomes more difficult between warmer surface waters and the cooler deeper waters , so phytoplankton are
“ Scientists have suggested seeding the ocean with iron to help actually cause blooms " drawn into warmer surface waters – along with nutrients such as nitrogen and phosphorus , which they need for their survival . This creates an environment in which phytoplankton can grow rapidly .
In optimal conditions of light , warmth and nutrient levels , the amount of phytoplankton can grow rapidly . Many species can double their number at least every day , leading to those species multiplying by 1000 times in only 10 days .
These blooms last until the nutrients are used up in the surface layers of the water column . In some places , there can also be autumn blooms , usually not as significant as the spring blooms , driven by nutrient input from autumn rains and reductions in the amount of sediment in the water . By winter , storms and water movement break down the layering of the water column , spreading phytoplankton from a warm stable layer into a colder , darker , deeper layer . This reduces their growth rates and leaves them waiting for the next spring .
As phytoplankton die , many reach the bottom of the sea and very slowly turn into soft rock , as mentioned earlier . As they reach the seafloor , however , they also do something else , and that ’ s lock away carbon . It ’ s been suggested that phytoplankton lock away between 30 and 50 billion metric tons of carbon annually , which is about 40 % of the global total . Phytoplankton assimilate more carbon when conditions are warmer and where there are plenty of nutrients available – for instance in bloom conditions . This has led to discussion over a number of years about how we could increase this amount of carbon that phytoplankton lock away .
Scientists have suggested seeding the ocean with iron to help actually cause blooms , and therefore removing more carbon . This could maybe be one more strand in slowing global warming . While seeding the ocean isn ’ t likely to happen anytime soon , we should all be aware about the essential role that these microscopic organisms already play in the world we are in .
So next time you ’ re muttering to yourself about brown snot in the water , try to remember that each annoying clump is part of a much wider system , and one that will be ever more important in regulating our climate and keeping levels of carbon under control . �
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